1. Field of the Invention
This invention pertains to welding machines, and more particularly to apparatus that manually regulates and visually indicates the output amperage of shunt controlled welding machines.
2. Description of the Prior Art
The output of some welding machines is regulated by a shunt that moves into and out of a transformer inside the welding machine case. The shunt is typically designed to be moved by a screw and nut arrangement. One end of a shaft protrudes through a first case panel and has a crank attached to it. The other end of the shaft has threads that mate with a nut on the shunt. Manually turning the crank causes the shunt to move linearly within the case. Examples of prior welding machines that employ a shunt and crank regulating system may be seen in U.S. Pat. Nos. 5,639,392 and 5,660,749. A generally similar welding machine is manufactured by Miller Electric Company, Appleton, Wis., under the trademark Thunderbolt.
To determine the shunt position relative to the transformer, and thus indicate the welding machine output amperage, it is known to include a wiper that is attached to the shunt. The wiper moves linearly inside the welding machine case with the shunt in response to turning the crank mounted on a shaft protruding from a first panel of the machine case. An elongated opening through a second panel of the machine case at a right angle to the first panel enables a person to see the wiper position. A scale on the outside of the case second panel adjacent the opening provides correlation between the shunt position and the welding machine output.
In another shunt controlled welding machine, there is an elongated rectangular opening in the same panel through which the crank shaft protrudes. The opening is at some distance from the crank. A long flexible band is attached at one end to the shunt and at a second end to a spring. In turn, the spring is connected to a stationary part of the welding machine. Manually turning the crank causes the shunt to move and also causes the band to slide within the opening. The band is marked in a manner that cooperates with a linear scale adjacent the opening to indicate the welding machine output in relation to the shunt position. An example of a prior shunt controlled welding machine having a crank and linearly moving indicator band on the same panel is a machine manufactured by Miller Electric Company, Appleton, Wis., under the trademark Econo Twin.
The prior shunt controlled welding machines provide excellent performance at an economical cost. Nevertheless, it is desirable that the mechanism for indicating the welding machine output be further developed.
In accordance with the present invention, a planocentric gear is provided that indicates the output amperage of a shunt controlled welding machine. This is accomplished by apparatus that includes a high gear reduction between a turnable handle and a revolving pointer.
The welding machine has a transformer inside a case. A shunt includes a threaded block. Threads on one end of a shaft mate with the block threads. The other end of the shaft extends through a panel of the case. Attached to the shaft outside of the case panel is the handle. By turning the handle, the shaft rotates to linearly move the shunt into greater or lesser engagement with the welding machine transformer.
The handle is formed with an annular recess partially defined by a hub external surface and by an internal annular surface. The hub external surface is concentric with the axis of rotation of the shaft. The handle internal annular surface is eccentric to the shaft axis of rotation.
Fixed to the case concentric with the shaft axis of rotation and within the handle recess is a pinion. Around the pinion outer diameter are a number of teeth. An inner diameter of the pinion loosely pilots over the hub external surface of the handle.
The planocentric gear further comprises an indicator that is also within the handle recess. The indicator has an outer diameter that fits with a running clearance inside the eccentric internal annular surface of the handle. The indicator also has a number of internal teeth that are concentric with the indicator outer diameter. The indicator teeth mesh with the pinion teeth. The indicator has at least one more tooth than the pinion. The pointer is part of the indicator and is outwardly directed from an outer periphery of the indicator. A scale is imprinted on the welding machine case around the shaft axis of rotation. The scale is calibrated to correlate welding machine output amperage with the position of the indicator pointer.
In operation, the welding machine operator turns the handle to obtain the desired output amperage from the welding machine. Turning the handle causes its eccentric internal annular surface to force the indicator to orbit about the shaft axis of rotation. Superimposed on the indicator orbiting is a revolving of the indicator about the shaft axis of rotation in the same direction as the handle turning, but at a much slower speed. Specifically, for each complete turn of the handle and corresponding complete orbit of the indicator, the indicator undergoes a partial revolution by advancing one tooth on the pinion. The indicator pointer thus revolves in proportion to the handle turns and indicates the welding machine output amperage from the scale imprinted on the case.
The method and apparatus of the invention, using a planocentric gear, thus provides a very economical way to indicate output amperage of a shunt controlled welding machine. The planocentric gear is on the same machine panel as the handle, thereby improving accessibility to and versatility in placement of the welding machine.
Other advantages, benefits, and features of the present invention will become apparent to those skilled in the art upon reading the detailed description of the invention.